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91.
The effect of extracellular inorganic phosphate on Na+ movements in dog red blood cells has been studied. As the phosphate concentration is increased from 0 to 30 mM, Na+ efflux increases by 2- to 3-fold and Na+ influx increases approximately 2-fold. This enhancement of Na+ fluxes by phosphate can be prevented by the addition of iodoacetate (1 mM), an inhibitor of glycolysis, or 4-acetamido-4′-iso-thiocyantostilbene-2,2′-disulfonic acid (0.01 mM), which blocks anion transport, to the medium. The increases in Na+ movements are not caused by changes in cell volumes. These results suggest that phosphate must enter the cell to enhance Na+ fluxes and that the mechanism of action may be via a stimulatory effect on glycolysis. 相似文献
92.
93.
Robert E. Hruska Karen T. Pitman Ellen K. Silbergeld Lynn M. Ludmer 《Life sciences》1982,30(6):547-553
Administration of prolactin to adult male rats, by s.c. injection, significantly increases the density of the striatal dopamine (DA) receptors, without altering the apparent affinity of the receptors for [3H]spiroperidol. Larger doses of prolactin are required to increase the density of the striatal DA receptors in hypophysectomized rates compared to normal rats. These results suggest that prolactin might be the common mediator of the increase in striatal DA receptor density produced by either estrogen or haloperidol administration. Monitoring and/or altering prolactin levels might be informative in neurologic or psychiatric disorders involving striatal DA neurotransmission. 相似文献
94.
The sterol diol fraction from the lipids of organ-pipe cactus, Stenocereus thurberi, was separated into five compounds: macdougallin, peniocerol, cyclostenol, stenocereol and thurberol. The last three compounds have not been described before. All compounds were characterized by physical and spectroscopic properties. 相似文献
95.
Ashis K. Sen Kalyan K. Sarkar Pronobesh C. Mazumder Nilima Banerji Raimo Uusvuori Tapio A. Hase 《Phytochemistry》1982,21(7):1747-1750
Three new tetraoxygenated xanthones (garcinones A, B and C), each disubstituted with C5-units, have been isolated from the chloroform extract of the fruit-hulls of Garcinia mangostana. Their structures were established by a combination of spectral interpretation and chemical correlation. 相似文献
96.
Carbamate kinase from Streptococcus faecalis is inactivated by butanedione in borate buffer, which implies the presence of an essential arginine at the active site of the enzyme. The inactivation reaction is first order in [butanedione] and a replot of the inactivation rate data infers that one arginine is modified. The enzyme is protected against inactivation by ADP, ATP, the metal-nucleotides and carbamyl phosphate but not by carbamate. Amino acid analyses reveal that one of three arginines is modified by butanedione in the absence of protecting agents, and the binding of ADP to the enzyme prevents modification. Thus, analysis of the data suggest that (i) substrate binding to arginine and (ii) protein conformational changes at the active site are responsible for protection of an essential arginine against modification by butanedione. 相似文献
97.
Frequency changes with time in vivo of radiation-induced chromosomal aberrations in skin fibroblasts
D. Couzin 《Mutation research》1979,60(3):367-380
5 Syrian hamster litter mates were each irradiated with X-rays on one flank to 300 rad. Skin biopsies were taken from both the irradiated and unirradiated (control) flanks of each animal at one day and at about 6 months after irradiation. The cells cultured from these biopsies were used to determine the frequencies of chromosomal aberrations. During the 6-month period there were significant reductions in the frequencies of both reciprocal translocations and terminal deletions.
Translocations involving the short arm of the Y-chromosome, however, showed a significant increase during this period.
It is possible that while the latter phenomenon was due to cell selection in vivo the general fall off in translocations and deletions was the result of a long term in vivo repair mechanism or perhaps the results of certain aberrations proving to be lethal with prolonged expression times. 相似文献
98.
Wen-Zong Whong 《Mutation research》1979,60(3):301-312
The nature of the N2 effect for ICR-170, i.e., the greater mutagenic and lethal activities of this agent in the presence of N2 than O2, has been studied at the ad-3 region of Neurospora crassa. The characteristics of the N2 effect for ICR-170 were that (1) the N2 effect with ICR-170 was displayed in conidia when N2 was administered during, but not before or after, ICR-170 treatment, (2) the highly increased mutagenic and lethal activities of ICR-170 in the presence of N2 were due to an anoxic condition rather than to the presence of N2 per se, (3) the high killing activity of ICR-170 under N2 was due largely to increased cytoplasmic inactivation, (4) the N2 effect was a general phenomenon at the ad-3 region of N. crassa, and (5) the highly ICR-170-induced mutation in conidia under N2 was attributable to an actual enhancement in the mutagenic activity of ICR-170 rather than to selective killing. With regard to the mechanisms of the N2 effect with ICR-170, results indicate that this effect (1) was not due to more extracellular oxidative degradation of ICR-170 molecules in the presence of O2, or to a greater uptake of ICR-170 by conidia under N2, but (2) was due to the inhibition of conidial respiration under an anoxic environment. 相似文献
99.
T Kuroki C Malaveille C Drevon C Piccoli M Macleod J K Selkirk 《Mutation research》1979,63(2):259-272
For optimum mutagensis in V79 Chinese hamster cells, the amount of liver postmitochondrial fraction in the assay was found to be of critical importance, depending on the chemicals being tested. Benzo[a]pyrene (BP) required lower (1-5%) concentrations of the liver 15 000 X g supernatant (S15) from methylcholanthrene pretreated rats for a maximum induction of cytotoxicity and mutagenicity, as determined by 8-azaguanine- and ouabain-resistance. A sharp peak of mutagenicity and cytotoxicity was induced by 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (7,8-diol BP) at a concentration of 1% of the S15 fraction. Little or no response was induced by these compounds with the S15 concentrations of more than 10%. Similarly, aflatoxin B1 induced a sharp peak of mutagenicity and cytotoxicity at a concentration of 2% of the liver S15 fraction from Aroclor-pretreated rats. Under the same condition, non-carcinogenic aflatoxin G2 did not induce cytotoxicity and mutagenicity. Analysis of BP metabolites by high-pressure liquid chromatography indicates that with the 30% S15 fraction, more than 80% of BP was metabolized during the first 15 min, while with the 2% S15 fraction, 7,8-diol BP increased continuously throughout the 120-min incubation period, suggesting a strong metabolic competition to rapidly remove BP and 7,8-diol BP with a high concentration of the S15. In contrast with these compounds, N-nitrosodimethylamine induced mutagenicity and cytotoxicity which increased linearly in proportion to the increasing amount of the S15 fraction from phenobarbitone- and Aroclor-pretreated rats. Various nitrosamines with different lipophilicity were examined at a high (30%) and low (2%) concentration of the S15 fraction from Aroclor-pretreated rats, in which ratios of mutation frequencies at 30% and 2% correlated inversely with lipophilicity of the compound. This result suggests that the lipid solubility of test compounds may be one factor which determines the concentration of post-mitochondrial supernatant for optimum mutagenesis. 相似文献
100.
K. K. S. BHAT 《Plant, cell & environment》1981,4(4):297-302
Abstract. The rates of uptake of 32 P-labelled orthophosphate by whole root systems of young apple trees (M.9 rootslocks and Worcester Pearmain seedlings) were measured in solution culture. Using a solution depletion technique, the 32 P-phosphate uptake rates per unit length, surface area or fresh weight of roots were determined as a function of 32 P-phosphate concentration in solution at the root surface over the range 0.25–10 mmol m−3 . The effect of P concentration within various plant parts on the relation between uptake rate and external P concentration was studied using plants differing in internal P levels.
The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m−3 . Fluxes, inflows and unit absorption rates increased approximately proportionately with solution concentration up to 10mmolm−3 . Except perhaps in the case of the low-P M.9 plant, there was no evidence of a diminishing returns type of relationship over the range of solution concentrations examined. The threshold P concentration in solution above which uptake rates cease to increase thus appears to be higher for apples than for other species.
At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low-P plants than for high-P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P. 相似文献
The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m
At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low-P plants than for high-P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P. 相似文献